I don't mind starting with a sort by name or time added. But then I'd like to move a few around. I'm going to make a web gallery, and somtimes want to tweak the order of presentation. is this possible?

Yes, you can establish a user sort order from a folder view (within the restrictions described). But - depending on your folder structure - there is often a need to include images from more than one folder in a Web Gallery or Slide Show. Also, when you base on a folder, the number of images in the folder could increase as you do more imports, whereas the content of a collection remains stable unless you add/delete to/from the collection.